The present invention relates to a curable composition having an improved pot life, and particularly relates to a curable composition comprising an organic polymer which contains at least one silicon-containing hydrolyzable group in the polymer molecule and a curing agent.
It has been known that vinyl resins containing a hydrolyzable silyl group at an end of the main chain or in a branched chain have not only the excellent properties of vinyl resins such as high gloss, weatherability and discoloring resistance, but also an improved adhesive property to inorganic materials due to the hydrolyzable silyl group. Further when crosslinked at normal temperature in the presence of water, particularly moisture in air, to form a dense network structure, the cured resins have excellent properties such as high chemical resistance, water resistance, heat stability hardness and weatherability (Japanese Unexamined Patent Publication (Tokkyo Kokai) No. 36395/1979). Though those vinyl resins containing a hydrolyzable silyl group (hereinafter referred to as "hydrolyzable-silyl group-containing vinyl resins") can be cured without a curing agent, in such a case, the curing step must carried out at a high temperature or the curing rate at a low temperature is slow. Accordingly the curing step is carried out in general at a low temperature with a curing agent, whereby excellent coating films having the above-mentioned properties can be obtained. The hydrolyzable-silyl group-containing vinyl resins can provide excellent cured resins by using a curing agent, as mentioned above. The vinyl resins, particularly vinyl resins which have a silyl group containing three hydrolyzable groups, however, have a problem in that when the resins are blended with a curing agent, the blended compositions have a shorter pot life, particularly pot life in open system. For improving the pot life of the vinyl resins, there was proposed, for instance, a process described in U.S. Pat. No. 4,043,953. In that process, pot life in the presence of a curing agent is improved by adding a hydrolyzable reactive silane monomer of the formula: EQU X.sub.k Si(OR).sub.4-k
wherein X is an organic group having 1 to 12 carbon atoms, R is an alkyl group having 1 to 5 carbon atoms such as methyl, ethyl, 2-methoxymethyl or 2-ethoxyethyl, "k" is 0, 1 or 2, to an organosilane polymer prepared by copolymerizing a monomer containing CH.sub.2 .dbd.C&lt; excepting a monomer containing an active hydrogen group such as hydroxyl group, carboxylic group or amido group with an organosilane monomer such as acrylate alkoxysilane, methacrylate alkoxysilane or vinylalkoxysilane, in which the amount of the hydrolyzable reactive silane monomer is 0.5 to 15% by weight on the basis of the organosilane polymer. The curing agent to be blended is an organic acid such as p-toluenesulfonic acid or n-butyl phosphate, a metal salt of organic acid such as tin naphthenate, dibutyltin dilaurate, iron stearate or lead octenoate, an organic amine such as isophoronediamine, methylenediamine or imidazole, and used in an amount of 0.1 to 5% by weight, preferably 0.2 to 1% by weight. In the Examples of the U.S. patent, measurement of pot life is conducted under conditions where a mixture of the organosilane polymer, the hydrolyzable reactive silane monomer and the curing agent is kept in a sealed container. Therefore, there is no description concerning the pot life in open system measured in the present invention, which is practically important. In fact, when measuring the pot life of the mixture described in the U.S. patent, i.e. a mixture of the organosilane polymer, the hydrolyzable reactive silane monomer and the curing agent, in open system, sufficient pot life can be obtained only when an organic amine is used. When other curing agents are used, the pot life in open system is short. There is also a problem in case an organic amine is used, however, in that the cured resin is colored due to the organic amine. Accordingly, development of another curing catalyst system has been desired.
From such viewpoint, there was proposed a curing catalyst system comprising a particular curing agent which contains an organotin compound (Japanese Unexamined Patent Publication (Tokkyo Kokai) No. 63351/1982), which shows technical progress in this art. However, a curing catalyst system having a high curing activity and a long pot life has not yet been developed.
As a result of the inventors' intensive study, a curable composition having a high curing activity and a long pot life has been found, and the present invention has been completed.